A Guide to Email Split Testing

|by Demi-Leigh Donohoe

Email split testing can be used to determine which version of an email campaign will perform the best.

Also known as A/B testing and multi-variant testing, split testing is a technique that marketers can use to improve email marketing performance.

The process involves sending two or more variants of an email to a small portion of subscribers.

The one which performs the best after a certain amount of time will win the split test, and this winning campaign will then be sent to the remaining subscribers.

In this post, we’ll talk you through split testing and the benefits you can reap from it.

Is email split testing really worth your time?

We’ve given you a basic overview of what split testing is, but why bother with it? Why spend your time creating two slightly different emails when you can just create one?

Maybe you’re happy with how your emails are performing and you don’t feel like they need any improvements.

Well, the truth is, nobody can get it right all of the time. As time goes on, your email list won’t stay static, and your subscribers’ preferences will change. So it makes sense to make regular changes to your email strategy, too.

If you want to keep your subscribers engaged and keep your unsubscribe rate down, you need to be regularly testing and trying different things when it comes to your emails. And sometimes it’s the little changes that can make the biggest difference.

That’s where split testing comes in.

Rather than relying on guesswork, one of the most effective ways of finding which techniques work best is to try them out. When you run split tests on your emails, there’s no doubting whether coincidence was at play or whether causation was the real reason for your sudden increase in click-through rates. You know that the single change you made is actually the thing that led to the change in performance.

Basically, email split testing gives you the opportunity to find out what your subscribers respond to and engage with.

You can then use knowledge this to finetune details in your email campaigns and ultimately make better, more data-driven marketing decisions.

How to decide what to test

If you’ve decided to start split testing your emails, you’re well on the way to email marketing success.

Now for the next step – deciding which elements of your email to test. Will it be replacing an image with another? A different coloured call-to-action? Reducing the amount of text?

Whatever you choose to test, we want to give you the ultimate split testing advice:

Only ever test one element of your email campaign at a time.

Split testing your emails is only effective if you isolate each element. If you choose to test a number of changes at once, you won’t be able to identify which change it was that impacted your performance.

Let’s take a look at which aspects of your email you can test.

Subject line

Your email’s subject line is the first thing your subscribers will see. It’s one of the most crucial elements of your campaign because it has a huge impact on your email open rate. Subscribers use the subject line to decide whether they want to bother looking at your email or not.

For a subject line to be effective, you must show your contacts the value of opening your email campaign.

Here are a few things you can experiment with to test your email subject lines:

Subject line length

According to Invescpro, the performance of subject lines vary according to subject line length.  Subject lines of 6-10 words perform best with an open rate of 21%. Longer subject lines of 21-25 words performed not so well, with an open rate of 9%.

Be concise. Shorter subject lines often work better because they get the message across more succinctly.

However, obsess about the length of your subject line at your own risk! The quality of what you say is more important than the quantity.

Using emojis

Emojis increase email open rates in some cases. However, when emojis fail, performance deteriorates.

You might wonder whether emojis would fit with your brand or for your specific audience. One way to find out is to trial the use of emojis in your subject lines in a split test.

Emoji or no emoji, you need to come up with a strong subject line for your email campaign.

This example from Rockett St George shows effective use of emojis in their subject line. The emoji fits naturally into the context of email.

Preheader text

The preview header text of your email will also have an impact on your open rate.

Split testing different preview text copy could help you identify what makes your subscribers choose to open your email campaign.

The preview text needs to support your subject line, working as a team to drive open rates upwards.

Including numbers and percentages

Have you ever felt more encouraged to buy something because you’ve seen it has lots of good reviews? This is social proof in action – the concept that people are more likely to do something if there’s evidence of other people doing it.

Citing numbers and percentages is an effective way of including social proof in your subject line -  it adds validity to the claims you’re making. This adds authority to your subject line copy.

Be careful - overusing numbers and percentages to make your point can come across as pushy or forced. A split test can reveal whether your numbers and percentages add enough value to the email subject line to really make a difference.

Personalisation techniques

Addressing your contact by name in the inbox makes them sit up and take notice, but only when done correctly.

With people receiving potentially hundreds of emails a day personalisation has never been so important and tactics as simple as personalised subject lines can increase open rates by 20 percent.

To use custom personalisation techniques, you need to look deeper into your data, perhaps looking at subscribers’ previous purchases, birthdays, or upcoming events.

As with any other technique, it’s worth trialling these techniques for yourself. A split test can be used to find what subject line techniques work the best with your specific audience.


‘It’s not what you say it’s the way that you say it’ is a popular phrase for a reason.

Subject lines need to stand out. Each subject line you write should be concise and original, differentiating it from the crowd.

Be aware of the perils of sounding boring or flat. You need your subject line to grab your readers’ attention and boost open rates.

An Invescpro study found that the words ‘Free’, ‘newsletter’ and ‘fw:’ caused a downturn in performance. They aren’t original, don’t give users true value, and appear ill-thought-out.

Subject lines are an opportunity to develop your brand. Once you’ve found a winning formula, slight tweaks to your future subject lines will yield great results.

Email content split testing ideas

Of course, testing your email subject lines is only the start. Testing the content that’s inside your actual email is just as important.

Take a look at some of the different elements of your email that you can test:

Email format

The way that you present information in an email can impact the way people interact with it.

The F-shaped reading pattern shows how people scan information on a screen and is a good guide for email marketers to follow.

Would a standardised design allow you to get your main message across with the level of creativity you need, or do you need to take an alternative approach?


The images and positioning of your images can help your recipients scan your emails quickly. This may be as simple as moving your image from above to below a paragraph.

Have you carefully considered where your images are placed in your email campaigns? Does their positioning complement the copy you use?


The position and wording of your calls-to-action can have an impact on your click-through and conversion rates.

Writing different call-to-action copy for a split test will improve the overall click-through rate of your email campaign when it’s distributed to the full mailing list.

Do you compel your readers to click through from your email campaigns with your current call-to-action copy, or could it be improved?

Amount of text

When conducting a split test, try reducing the amount of copy you write. The purpose of your email is to drive your recipients towards an action. The longer they have to spend reading your email campaign, the less likely they are to act.

Would you be able to get your message across in a few short paragraphs, or does longer-form content work better for your brand?

How big should your list sample size be?

When carrying out a split test, you need to choose a sample of your email list to send your emails to. 

The larger the split test, the more reliable your results will be. However, increasing the size of your split test also means that more people will receive an unoptimised campaign.

It’s a balancing act.

Use your common sense to identify whether your split test takes into account a large enough cross-section of your list.

If you only want to send your split test to a small number of subscribers, you have to remember that your split test is statistically viable.  As your email marketing list gets smaller, the value in the results of a split test decline. If you need to send an email to a very small segment of your list, take a look at previous campaign data and trust your instincts.

We suggest that, for a split test to work, your minimum list size should be at least 1000.  However, even then, your results won’t be as reliable as they would with a much larger list.

How long should you split test take?

Think about the amount of time that you wait before analysing the results of your split test. If you’re eager to send your email, it can be tempting to perform a split test over a very short period of time.

The problem with this is obvious.

If your subscribers don’t check their emails straight away then your results will be skewed. Make sure that you plan enough time in between sending the split test and making any decisions. Don’t be tempted to declare your results early.

Once you have identified the best variant of your campaign, you can send the campaign to the rest of your mailing list.

If you’re planning to perform several split tests, you need to have a longer amount of time to wait and a larger email list.

Analysing your split test results

With so many elements to test, there are several options for measuring the success of email variants. Your task is to decide which metrics are most important to your performance.

Sure, we know that everybody wants to achieve higher revenue from their emails, but what specifically do you want to achieve with your email split test?

Most email marketing platforms provide a wealth of data that will help you gauge the performance of your email marketing campaigns.

The key is to think back to your email marketing goals. Your goals will tell you what email marketing metrics you should focus on - such as delivery rate, open rate, or click rate – and what you should work on improving.

Top tips for split-testing your emails

Here are some top tips to help you get started with email split testing:

Test one element at once

We can’t stress this enough!

If you test several elements of your email at once, one email might perform a lot better than the other, but you won’t know the exact reason why.

The only way to determine which elements of your email campaign altered your performance is to isolate each one in turn.

Decide what you’re going to test before creating your email

Don’t decide to do a split test at the last minute.

You should plan your split test before you started the creation process. This will save you lots of confusion in the testing stage.

Identify your goals

Know what it is you’re aiming for with your email split test.

If you’re optimising your subject line, know that you should be looking for changes in open and spam rates. Any other improvements are a bonus but they shouldn’t affect your final decision.

Plan time for split testing

If you rush the split testing process, this will have an impact on the accuracy of your results.

You need to send your email split test to a small portion of your email list, and then you must wait. Give your subscribers enough time to receive and react to your split test before judging the results.

Choose the right email marketing platform

For effective email split tests, you’ll need to invest in an email marketing platform with split testing functionality.

Platforms like Conesso enable you to test just about any element of your email – subject line, text, colours, images, templates, preheaders, CTAs, and more.

Get started with email split testing

As you have seen, split testing your email marketing campaign is a great way to fine-tune your emails and improve campaign performance.

Marketers have a huge number of decisions to make when creating email campaigns, and it’s easy to become overwhelmed. Split tests can help by providing invaluable insights into what kind of emails resonate with your subscribers, so you can feel confident that you’re giving them what they want.

With Conesso, you can eliminate any guesswork and make better marketing decisions by running split tests on any elements of your emails. Try out different subject lines, copy, images, and templates, and we’ll help you see what works best. Book a demo today.

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